Most windrowers on the market all have some type of hydraulic header flotation. These types of flotation systems suspend the header from the windrower so that there remains a small percentage of the header mass supported by the ground. The advantages to these types of hydraulic float systems include the ability to easily adjust to a wide range of header weights/types, full adjustability of flotation system from the cab, few moving parts, compact, has built in dampening effects and is well received in the market.
However, due to internal friction of the cylinder seals of the flotation cylinders, these systems typically have poor ground following capabilities unless the mass supported by the ground is significant, in the order of 15% of the header mass. With this level of ground pressure (mass of header carried by the ground), wear on the ground contacting components is significant. Also, when hitting an obstacle, a higher ground pressure is undesirable.
In the traditional hydraulic float systems, the header float cylinders are each connected to a respective accumulator, pressure sensor and pressure control valve. The pressure control valves are in turn connected to a hydraulic pressure source such as a load sense pump. The controller receives input signals from the pressure sensors and makes adjustments to the pressure control valves to maintain a known pressure in the accumulator/cylinder circuit. The accumulator/cylinder system acts much like a spring so that when the header hits an obstacle and needs to go over the obstacle, the accumulator supplies pressure and flow to the cylinder to aid the movement of the header. When the header needs to go down into a ditch or low spot, the float cylinder drives oil back into the accumulator.
MacDon has traditionally maintained a coil spring flotation system that does not have the same friction limitations and typically has better ground following capabilities. A typical MacDon spring flotation system can achieve ground pressure in the order of 10% of the header mass while still having acceptable ground following capabilities. The spring flotation systems are currently used on MacDon windrowers and combine adapters.
Header flotation systems typically use a fluid circuit including an accumulator, hydraulic cylinders, and control valves to perform the flotation function. The vehicles may have a single hydraulic cylinder, or one on each side of the header, to perform both a lift and flotation function, or they may have separate hydraulic cylinders for the lift and flotation functions with the capability of independently adjusting the flotation force for each side of the header. Typically the operator selects the desired flotation setting by actuating rocker switches; wherein one switch position reduces header contact force with the ground, and another position increases header contact force with the ground. Once the flotation setting is selected, the control valves will return to this preset flotation condition whenever the flotation mode is selected, regardless of subsequent header lift and lower operations.
One aspect of the operator selected flotation setting is that it determines how quickly the header returns in a controlled acceleration or controlled “fall” to its terrain contact position after rising in response to contact with an elevated feature of the terrain. If the header falls too slowly, regions of the field may not be cut at the desired height. If the header falls too rapidly, however, the header may impact or ride roughly over the ground, thereby resulting in undesirably harsh or jarring ride characteristics. It is also possible that the header could impact the ground in some conditions, such as uneven terrain, with sufficient force to result in damage to the header and/or the crop. Typically, an operator's flotation setting will be a function, at least in part, on the ground speed of the vehicle. As a general rule, when traveling over a field of uneven terrain at a relatively low speed, terrain following can be achieved at slower header accelerations, compared to a higher speed. Thus, for travel at lower speeds, an operator would likely use a flotation setting to allow the header to fall more slowly than that selected for a higher speed.